1. Field of the Invention
The present invention relates to a control apparatus for fuel cell for obtaining electric power by an electrochemical reaction between fuel gas obtained by a reforming reaction of a reformate fuel, and an oxidizing gas, and more particularly to an apparatus for controlling the supply amount of reformate fuel or supply amount of oxidizing gas. This invention also relates to a method of controlling a fuel cell using the apparatus.
2. Description of the Related Art
A fuel cell is a kind of energy transformer for inducing an electrochemical reaction between a fuel gas such as hydrogen gas and an oxidizing gas such as oxygen gas in air, through an electrolyte, and picking up the generated electromotive force to the outside. Depending on the variety of electrolyte, polyelectrolyte fuel cell, phosphate fuel cell, solid electrolyte fuel cell and others are known, and in particular the polyelectrolyte fuel cell has many advantages such as low reaction temperature, and is highly expected to be used as a driving source for vehicles.
The power generation efficiency of these fuel cells varies with the temperature or humidity of the electrolyte, and the output increases depending on the supply amount of the fuel gas and oxidizing gas, and therefore in order to produce a required electric quantity efficiently, it is important to control the running conditions and the supply gas amounts. Relating to the oxidizing gas, for example, the oxidizing gas and fuel gas react with each other according to their composition, and if the oxidizing gas is supplied in excess of the fuel gas, the output of the fuel cell is not increased. On the contrary, however, the power required to supply the oxidizing gas may lower the power generation efficiency of the entire system, or the excessive oxidizing gas may cool the electrolyte to lower the power generation efficiency. It is hence needed to supply the oxidizing gas into the fuel cell depending on the required output.
For example, in the invention disclosed in JP No. 60-216467, by making use of the discharge pressure-discharge air flow curve of the compressor for feeding air to the fuel cell, and the voltage-current density curve of single cell (single battery), the air flow to be supplied into the cathode electrode in partial load operation of the fuel cell is calculated, and the control valve provided at the discharge side of the air compressor is controlled so as to be adjusted to the calculated air flow. That is, when the output current density is lowered, the discharge amount of the air compressor is lowered, and the discharge pressure is raised at the same time, and therefore the single cell voltage is raised and the power generation efficiency is enhanced.
In this related apparatus, along with changes of the required output in the fuel cell, the supply air flow and its pressure are varied, but the air supply state in the cathode electrode of the fuel cell and the air discharge state from the air compressor do not always coincide with each other. That is, when supplying air into the cathode electrode in the fuel cell from a supply device such as air compressor (air pump), an inevitable control delay occurs due to external factors such as flow resistance in a path of air supply, or expansion or contraction due to temperature changes. Besides, the fuel gas supplied into the fuel cell may not always coincide exactly with the required output of the fuel cell. Accordingly, if the output of the fuel cell changes and it is desired to change the supply amount of air or oxidizing gas accordingly, the supply amount of the oxidizing gas does not change by following the output of the fuel cell, and excess and insufficient supply amount of oxidizing gas occur alternately, and the output of the fuel cell may be unstable. Or, by supplying the oxidizing gas excessively, more power is consumed than necessary, which may lower the power generation efficiency of the entire system.
The invention is devised in the light of the drawbacks discussed above, it is hence an object of the invention to provide a control apparatus capable of enhancing the substantial power generation efficiency of a fuel cell, and stabilizing the output of the fuel cell easily.
To achieve the object, a first aspect of the invention relates to a fuel cell control apparatus which includes a fuel cell for producing electric energy, a physical quantity controller for controlling a physical quantity based on an output quantity in order to control the output quantity of the electric energy, a smoother for smoothing the output related quantity relating to the output of the fuel cell, and a physical quantity determining device for determining the physical quantity on the basis of the smoothed output related quantity.
In the first aspect of the invention, the quantity relating to the output such as output demand amount of fuel cell is smoothed by the smoother. This is, for example, a process of accumulating the output related quantities for a specific time, and determining the average, or a process of setting the intermediate value of the deviation of the present value and the target value after change for a specific time when the output related quantity is changed. Accordingly, since the physical quantity for determining the output quantity of the electric energy produced from the fuel cell is changed by following the smoothed output related quantity, neither shortage nor excess of supply amount of physical quantity occurs.
Preferably, the physical quantity determining device determines the amount of oxidizing gas reacting with the fuel gas to be supplied in the fuel cell, as the physical quantity. As a result, the output related quantity of the fuel cell, as the decisive factor of the supply amount of the oxidizing gas, is smoothed, and the output related quantity does not include temporary increase or decrease, and variation of the supply amount of oxidizing gas is suppressed, so that the output of the fuel cell is thereby stabilized.
In addition, the first aspect of the invention may further include a reformer for generating the fuel gas to be supplied to the fuel cell by a reforming reaction of reformate fuel, and the physical quantity determining device may control the amount of reformate fuel to be supplied to the reformer as the physical quantity. As a result, sudden change of command value of reformate fuel supplied to the reformer is suppressed, and irregular variations of control are prevented.
In addition, the first aspect of the invention may also include a adjuster for adjusting the reformate fuel amount determined by the reformate fuel determining device, according to the relation between the value obtained by the smoother and the output related quantity at a given moment. As a result, for example, if the deviation between the output related quantity at a given moment and the smoothed value of the output related quantity is large, the reformate fuel amount to be supplied to the reformer is adjusted. More specifically, the quantity determined by the reformate fuel determining means is adjusted by increasing or adjusted by decreasing. Accordingly, as compared with the reformate fuel amount determined only on the basis of the smoothed value, the reformate fuel amount is increased or decreased, and hence the response of the reformer is improved.
A second aspect of the invention relates to a fuel cell control apparatus which includes a fuel cell mounted on a vehicle as a driving power source, for producing electric energy generated by reaction between fuel gas and oxidizing gas, an acceleration or deceleration degree detector for detecting the manipulation amount relating to the acceleration or deceleration by the driver of the vehicle, and an oxidizing gas feed determining device for determining the supply amount of oxidizing gas to the fuel cell, on the basis of the manipulation amount detected by the acceleration or deceleration degree detector.
According to the second aspect, when the driver accelerates or decelerates the vehicle, the supply amount of the oxidizing gas to the fuel cell is increased or decreased accordingly, so that the output of the fuel cell suited to the driver""s request for acceleration or deceleration may be obtained.
In addition, the second aspect of the invention may further include an oxidizing gas adjuster for adjusting the supply amount of the oxidizing gas on the basis of the reforming response which is the generated state of the fuel gas, relative to the reformate fuel supplied in the reformer. As a result, when determining the supply amount of the oxidizing gas on the basis of the amount of the reformate fuel supplied in the reformer, the supply amount of the oxidizing gas, which should correspond to the a mount of fuel gas supplied in the fuel cell, is determined in consideration of the response when the reformate fuel i s reform ed into fuel gas, and therefore the supply amount of the oxidizing gas corresponds more accurately to the supply amount of the fuel gas, and an excess or a shortage of supply amount of oxidizing gas is avoided. The output of the fuel cell is, thus, stabilized.
A third aspect of the invention relates to a fuel cell control apparatus which comprises a fuel cell for producing electric energy generated by reaction between fuel gas and oxidizing gas, a reformer for generating a fuel gas to be supplied into the fuel cell by reforming reaction of reformate fuel, a reformate fuel detector for detecting the amount of reformate fuel to be supplied into the reformer, and an oxidizing gas feed determining device for determining the supply amount of oxidizing gas to the fuel cell on the basis of the amount of reformate fuel to be supplied to the reformer.
According to the third aspect, since the amount of fuel gas generated by reforming reaction in the reformer corresponds to the amount of reformate fuel supplied in the reformer, by determining the supply amount of the oxidizing gas on the basis of the amount of the reformate fuel, the amount of oxidizing gas corresponding to the fuel gas is obtained.
The fuel cell control apparatus of the first to third aspects of the invention may also include an oxidizing gas feed adjuster for adjusting the supply amount of oxidizing gas to the fuel cell on the basis of the utility rate of the oxidizing gas in the fuel cell. According to this constitution, the whole amount of the oxidizing gas supplied into the fuel cell is not spent for reaction, but partially used for reaction with fuel gas, and therefore the supply amount of the oxidizing gas is adjusted according to its utility rate, so that the supply amount of the oxidizing gas may be further optimized.
Preferably, the fuel cell has an electrode to which an oxidizing gas is supplied, and it may further include a temperature related quantity detector for detecting the physical quantity relating to the temperature at the electrode, and an oxidizing gas feed adjuster for adjusting the supply amount of the oxidizing gas on the basis of the physical quantity relating to the temperature near the electrode detected by the temperature related quantity detector. Therefore, since the supply amount of the oxidizing gas is adjusted according to the physical quantity relating to the temperature at the electrode for inducing a substantial reaction of oxidizing gas and fuel gas, error of supply amount due to expansion or contraction of oxidizing gas is corrected, so that the supply amount of the oxidizing gas may be more accurately controlled.
The fuel cell may further include a pump for supplying an oxidizing gas, a pressure related quantity detector for detecting the physical quantity relating to the pressure near the electrode, and an oxidizing gas command adjuster for adjusting the command value to the pump on the basis of the physical quantity relating to the pressure near the electrode detected by the pressure related quantity detector. Therefore, since the supply amount of the oxidizing gas is adjusted according to the physical quantity relating to the pressure near the electrode for inducing a substantial reaction of oxidizing gas and fuel gas, that is, at the supply point of oxidizing gas, error of supply amount due to expansion or contraction of oxidizing gas is adjusted, so that the supply amount of the oxidizing gas may be more accurately controlled.